Getting the Best Telecoil Response
A properly designed telecoil gain and frequency response along with proper orientation in the hearing aid can allow a user to hear well on the phone with either a pre-amplified (active) or non-pre-amplified (passive) telecoil. At Qualitone we designed our Marquise and Avail products to perform better with the pre-amplified (active) telecoils. This particular type of telecoil was selected for its signal-to-noise ratio and cell-phone immunity performance. Our manufacturing process orients the telecoil perpendicular to the faceplate for optimal sensitivity in custom products. The BTEs are standard products (not custom built) so the telecoil orientation has already been optimized by the initial product design process.
When selecting a product for its telecoil response, the best thing for the audiologist to do is to check the manufacturers telecoil specifications to see which products have a strong telecoil. The ANSI measurement for telecoil performance is measured within a range of frequencies between 200 and 5000 Hz. The resulting curve is called the "Sound Pressure Level for an Inductive Telephone Simulator" (SPLITS). An additional measurement: "High-Frequency Average" of the SPLITS curve (HFA-SPLITS) is the average SPLITS value at 1000, 1600, and 2500 Hz.
When you are looking for a powerful telecoil, the higher the SPLITS or HFA-SPLITS the stronger the telecoil will be. For example the Qualitone Marquise ITE Specifications show HFA SPLITS at 90-103 dB SPL and 107 dB SPL for the BTE. This indicates that the BTE has a more powerful telecoil than the custom device. The Advantage XP power directional BTE has an HFA-SPLITS of 113 dB SPL, clearly a much more powerful telecoil than what is available in a standard BTE. Thus, by using the HFA-SPLITS values, the selection of the proper telecoil becomes a much easier task. Finally, it is important to remember that not all telephones are created equal. If a particular telephone has very low magnetic radiation, then it still may be hard to hear even with a hearing aid having a properly designed, strong telecoil. Sometimes a change of telephones may be in order to improve the telecoil performance,